1. Field of the Invention
This invention relates to a mechanical writing implement, and more particulary, to an improvement in the fitting structure of the implement permitting the same to be easily assembled.
2. Description of the Prior Art
A writing implement of the type disclosed in Korean Utility Model Nos. 78-555 and 84-238, which corresponds to U.S. Pat. No. 4,136,980, issued Jan. 30, 1979, both granted to the present inventor, comprises a pencil barrel made of a synthetic resin provided with a single spiral groove on the inner wall thereof; a cap rotatably fitted to one end of the barrel; a carrier provided with a rounded spiral guide on the outward surface thereof, the spiral guide being engaged with for travelling along the spiral groove formed on the inner wall of the barrel to force a pencil lead to move forward or backward; a rotatable tip. And an elongated supporting member on the cap, or tip which cooperates with the carrier. When the cap, or tip, is rotated in one direction, the carrier moves the pencil lead out of the tip opening for use. Similiary, when the cap, or tip, is rotated in the opposite direction, the pencil lead is drawn into the barrel for storage.
The above writing implement, however, has a drawback in that the single spiral groove formed on the inside of the barrel can not be easily aligned with the corresponding spiral protrusion formed on the outward surface of the carrier when the carrier is assembled to the barrel. In addition, a relatively low pitch of the spiral groove of the barrel does not permit the tip, provided with a corresponding single spiral protrusion, to be firmly fitted to its proper position in the one end of the barrel, but it may be accidently disengaged from the barrel in use. For this reason, it is required to provide a special screw thread with dense pitch both in the inside of the barrel and on the outward surface of the inserted portion of the tip so as to secure a firm fitting. This is likely to add to the manufacturing cost in terms of the additional process that is required to form the special screw thread with the dense pitch. In this case, the external screw thread thus formed on the tip also can not be easily aligned with the internal screw thread formed in the inside of the barrel. In addition, a workman must rotate the tip by a full ten rotations provided that the tip has a special screw thread, for example with ten pitches, in order to attain a complete and firm fitting of the tip into the barrel. This also tends to increase the labor cost, thereby adding to the manufacturing cost.